This invention relates to electrochemical battery cells and, in particular, the manufacture of a lithiated cathode for use in such electrochemical battery cells wherein the cathode is manufactured from a lithiated vanadium complex having a cage structure.
The demand for improved energy storage devices such as electrochemical batteries has increased steadily. The recent trend towards smaller and lighter electronic devices has precipitated the demand for portable electronic equipment, where expense, durability, reliability and high energy density are critical.
Non-aqueous lithium electrochemical cells typically include an anode, an electrolyte prepared from a lithium salt dissolved in one or more organic solvents and a cathode of an electrochemically active material, typically a chalcogenide of a transition metal. During discharge, lithium ions from the anode pass through the electrolyte to the electrochemically active material of the cathode where the ions are taken up with the simultaneous release of electrical energy. During charging, the flow of ions is reversed so that lithium ions pass from the electrochemically active cathode material through the electrolyte and are plated back onto the lithium anode.
U.S. Pat. Nos. 4,751,157 and 4,751,158 to Uchiyama et al. disclose cathode materials for use in lithium electrochemical cells. The cathode material comprises a mixed metal oxide as an active material, along with a conductive diluent and a binder which is pressed into electrodes on a nickel screen and sintered under vacuum. The cathode materials are used in cells which contain a liquid electrolyte, and more particularly, those which contain LiAsF.sub.6 in an aprotic solvent, such as methyl formate.
U.S. Pat. No. 4,416,915 to Palmer et al. discloses a chalcogenide cathode made by applying a slurry of a mixture containing at least one intercalatable layered transition metal chalcogenide, a conductivity enhancing agent and a binding agent in a vehicle, to a high porosity current collector substrate. The cathode material is utilized in a non-aqueous lithium cell having an electrolyte comprising an electrolyte-solvent mixture.
U.S. Pat No. 4,560,632 to Alberto discloses a molded porous cathode collector for use in non-aqueous cells. The collector includes a particulate carbonaceous conductive material bonded with a suitable binder, and having on its surface a coating of a vinyl polymer film to improve its mechanical strength and handling characteristics. The cathode collector is used in association with liquid cathode materials.
Solid state rechargeable electrochemical cells constructed of an alkali metal foil anode, such as lithium foil, an ionically conducting polymeric electrolyte and a composite cathode containing a finely divided transition metal oxide are described extensively in the patent literature. See, for example U.S. Pat. No. 4,303,748 to Armand; U.S. Pat. No. 4,589,197 to North; U.S. Pat. No. 4,547,440 to Hooper et al; and U.S. Pat. No. 4,228,226 to Christian. U.S. Pat. No. 5,690,703 to Mitchell et al., discloses a carbon anode such as coke or graphite intercalated with lithium ions.
As discussed by Uchiyama et al., supra, rechargeable batteries employing lithium systems offer the potential for both high energy and light weight. While lithium intercalating transition metal oxides are attractive because of their tendency to possess high energy content, the known oxides are either expensive to prepare as in the case of vanadium oxides or they are electronic insulators thereby preventing their use for high battery current applications. Another difficulty with transition metal oxides, especially V.sub.2 O.sub.5, is susceptibility to over-discharge which results in structural rearrangement and severe losses in cell capacity.
Accordingly, there exists a need for an improved cathode possessing high ionic and electronic conductivity as well as good mechanical strength and improved recharge ability for use in electrochemical batteries.